This invention relates to a weaving loom, and more particularly to the detection of weft in a shuttleless loom.
Various weft detecting devices have been provided to detect whether or not a weft inserting apparatus has favorably completed its function of weft inserting for each of the weft yarns in a shuttleless loom, for example, such as an air-jet loom.
Also, an air-jet loom has been known in which a notch is formed in each of dents wherein is found a reed so that a weft guide passage is provided in the reed. To detect weft inserted through the guide passage formed in the reed, it has been known to mount a weft detecting device on the reed at a position between a cloth selvage and a waste selvage, such device including a photoelectric detection unit emitting and receiving a light beam passing across the weft guide passage. This device is disposed so as to ride on the dent or dents, which is or are within a region subject to substantial influence of an air-jet stream injected from an air-jet nozzle closely adjacent to the cloth selvage, thereby causing vibrations of a portion of the inserted weft present in the dent or dents, on which the device rides, to facilitate detection of the weft by means of the detection unit.
However, such a weft detecting device would not be favorably applicable to an air-jet loom, such as those shown in U.S. Pat. Nos. 4,085,777 and 4,150,699, wherein a weft is inserted through a guide passage provided in a series of guide plates located in front of a reed. This air-jet loom requires removal of the inserted weft from the guide passage, while the afore-mentioned type of air-jet loom, wherein the weft is inserted through the guide passage formed in the reed itself, does not require the weft to be removed from the guide passage, since the weft beating is carried out with the weft maintained at a fixed position in the guide passage.
Furthermore, German Pat. No. 2,105,559 and U.S. Pat. Nos. 4,085,777 and 4,150,699 each disclose a weft detection device applied to an air-jet loom of the afore-mentioned type, wherein the weft is inserted through the guide passage, formed in the guide plates, and then removed therefrom. Each of these detection devices has a detection unit incorporated in the guide plate itself so as to allow a light beam emitted by the detection unit to pass across the narrow exit slot defined by the associated guide plate. It will be therefore understood that these known devices are adversely affected by vibrations of the guide plate in which they are incorporated and a number of guide plates each incorporating the detection unit must be provided to allow for changes in the width of a cloth. Furthermore, it is required that each guide plate with the detection unit be of a relatively great thickness to have the detection unit incorporated therein, possibly causing additional disadvantages.